[PATCH v3 12/13] mm/huge_memory: add and use normal_or_softleaf_folio_pmd()

Lorenzo Stoakes (Oracle)
2026-03-20T18:08:09Z

Now we have pmd_to_softleaf_folio() available to us which also raises a
CONFIG_DEBUG_VM warning if unexpectedly an invalid softleaf entry, we can
now abstract folio handling altogether.

vm_normal_folio() deals with the huge zero page (which is present), as well
as PFN map/mixed map mappings in both cases returning NULL.

Otherwise, we try to obtain the softleaf folio.

This makes the logic far easier to comprehend and has it use the standard
vm_normal_folio_pmd() path for decoding of present entries.

Finally, we have to update the flushing logic to only do so if a folio is
established.

This patch also makes the 'is_present' value more accurate - because PFN
map, mixed map and zero huge pages are present, just not present and
'normal'.

Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
---
mm/huge_memory.c | 47 +++++++++++++++++++----------------------------
1 file changed, 19 insertions(+), 28 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9ddf38d68406..5831966391bd 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2342,10 +2342,6 @@ static void zap_huge_pmd_folio(struct mm_struct *mm, struct vm_area_struct *vma,
add_mm_counter(mm, mm_counter_file(folio),
-HPAGE_PMD_NR);

- /*
- * Use flush_needed to indicate whether the PMD entry
- * is present, instead of checking pmd_present() again.
- */
if (is_present && pmd_young(pmdval) &&
likely(vma_has_recency(vma)))
folio_mark_accessed(folio);
@@ -2356,6 +2352,17 @@ static void zap_huge_pmd_folio(struct mm_struct *mm, struct vm_area_struct *vma,
folio_put(folio);
}

+static struct folio *normal_or_softleaf_folio_pmd(struct vm_area_struct *vma,
+ unsigned long addr, pmd_t pmdval, bool is_present)
+{
+ if (is_present)
+ return vm_normal_folio_pmd(vma, addr, pmdval);
+
+ if (!thp_migration_supported())
+ WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
+ return pmd_to_softleaf_folio(pmdval);
+}
+
/**
* zap_huge_pmd - Zap a huge THP which is of PMD size.
* @tlb: The MMU gather TLB state associated with the operation.
@@ -2390,36 +2397,20 @@ bool zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
tlb->fullmm);
arch_check_zapped_pmd(vma, orig_pmd);
tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
- if (vma_is_special_huge(vma))
- goto out;
- if (is_huge_zero_pmd(orig_pmd)) {
- if (!vma_is_dax(vma))
- has_deposit = true;
- goto out;
- }

- if (pmd_present(orig_pmd)) {
- folio = pmd_folio(orig_pmd);
- is_present = true;
- } else if (pmd_is_valid_softleaf(orig_pmd)) {
- const softleaf_t entry = softleaf_from_pmd(orig_pmd);
+ is_present = pmd_present(orig_pmd);
+ folio = normal_or_softleaf_folio_pmd(vma, addr, orig_pmd, is_present);
+ if (folio)
+ zap_huge_pmd_folio(mm, vma, orig_pmd, folio, is_present,
+ &has_deposit);
+ else if (is_huge_zero_pmd(orig_pmd))
+ has_deposit = !vma_is_dax(vma);

- folio = softleaf_to_folio(entry);
- if (!thp_migration_supported())
- WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
- } else {
- WARN_ON_ONCE(true);
- goto out;
- }
-
- zap_huge_pmd_folio(mm, vma, orig_pmd, folio, is_present, &has_deposit);
-
-out:
if (has_deposit)
zap_deposited_table(mm, pmd);

spin_unlock(ptl);
- if (is_present)
+ if (is_present && folio)
tlb_remove_page_size(tlb, &folio->page, HPAGE_PMD_SIZE);
return true;
}
--
2.53.0